This present invention relates to three-dimensional imaging. In particular, the present invention relates to scanning a three-dimensional volume with a two-dimensional array of acoustic transducer elements.
Typical aperture sizes for two-dimensional diagnostic ultrasound transducers range anywhere from 30 wavelengths by 30 wavelengths up to 30 wavelengths by 200 wavelengths. For example, a two-dimensional array has on the order of 60 by 60 to 60 by 200 spatial sampling locations or elements. Such two-dimensional arrays have from 4,000 to 12,000 elements.
Typical high performance medical diagnostic ultrasound systems have about 200 beamforming channels and an associated 200 signal conductors in the transducer cable connecting the beamforming channels to the transducer array. Currently, 4,000 transmission lines are not provided in a clinically useful cable. Current ultrasound systems and transducers may not be capable of real-time electronic, fully sampled three-dimensional beamformation without significantly sacrificing image quality or clinical usefulness.
An alternate approach to three-dimensional imaging uses beamforming electronics within the transducer to avoid a large number of transmission lines in the cable or a large number of beamforming channels in the system. However, the circuitry located in the transducer has a high degree of complexity in terms of both the number of circuit functions, number of components and cost.
Another approach uses a sparse array for three-dimensional imaging to reduce the number of transmission lines used in a cable. U.S. Pat. No. 6,279,399 uses a combination of a sparse array for three-dimensional imaging and a configuration of elements for two-dimensional imaging. A set of mode switches or multiplexers configure the transducer elements to form either a one-dimensional array providing a two-dimensional scan mode or a two-dimensional sparse array providing a three-dimensional scan mode. In the two-dimensional scan mode, the length of the sparse elements is extended in one direction, forming a conventional one-dimensional array for two-dimensional images in a single fixed image plane. However, sparse arrays for three dimensional imaging have poor sensitivity and contrast resolution.
In U.S. Pat. No. 5,563,346, three-dimensional scanning is provided using a minimum number of signal lines. A two-dimensional array operates as a linear, annular array to form beams normal to the array surface at different locations on the two-dimensional array. Concentric rings of elements are interconnected using a multiplexer or switching. Each concentric ring represents common delay areas for beamforming, so connects with a single signal line. However, the normal beam constraint limits the volume which can be scanned by the aperture size and shape of the two-dimensional array.
The present invention is defined by the following claims, and nothing in this section should be taken as a limitation on those claims. By way of introduction, the preferred embodiments described below include methods and systems for electronically scanning within a three dimensional volume while minimizing the number of system channels and associated cables connecting a two-dimensional array of elements to an ultrasound system.
An array of semiconductor or micro-machined switches electronically interconnects various elements of the two-dimensional array. Elements associated with a substantially same time delay are connected together as a macro element, reducing the number of elements to be connected to beamforming or system channels. To beam form in the desired direction, the macro elements are configured as a phased array or along substantially straight lines in at least two dimensions (i.e. along the face of the two-dimensional transducer). Such macro elements allow transmission and reception along beams that are at an angle other than normal to the two-dimensional transducer array. Beams at such angles may be used to acquire information beyond the azimuth and elevation extent of the two-dimensional array.
Various configurations of macro elements are possible. For example, the macro elements in each configuration are parallel across the two-dimensional array, but different configurations are associated with rotation of the macro elements such that each configuration is at a different angle on the two-dimensional array. As another example, the macro elements are configured in a plurality of separate rows of parallel macro elements (i.e. configured as a 1.5D or 1.75D array of macro elements). As used herein, a 1.25D array includes arrays using a center row of elements short in the elevation extent for close focal regions and longer in elevation extent for farther focal regions, 1.5D array includes three or more rows of elements where the outside rows in opposing side pairs are each connected to the same beamformer channels and 1.75D includes independent operation of a plurality of rows of elements.
In one embodiment, two or more switches are provided for each system channel, allowing for rotation of macro elements. The different rotation positions of macro elements defines different two-dimensional scan planes within the three-dimensional volume. Two, three or more switches are provided for each element to interconnect the elements in many possible combinations.
Any one or combinations of any two or more of the aspects discussed above may be used. Further aspects and advantages of the invention are discussed below in conjunction with the preferred embodiments.